Split casting steam chest, nozzle chamber and casing assembly for turbines

ABSTRACT

In an elastic fluid turbine, an improved construction of the casing, the steam chest and the nozzle chamber which permits free expansion of parts subject to thermal transients at reduced cost and higher assurance of quality. This is accomplished by casting the nozzle chamber, the upper and lowe halves of the outer casing and at least a portion of the steam chest as separate pieces and then bolting them together. In cases where a high pressure nozzle chamber is employed, this also is cast separate from the lower casing half and fitted into an opening in that part. Forming the assembly from a number of parts in this manner considerably reduces the problems encountered in casting complex shapes which are costly and difficult to fabricate.

United States Patent Dinenno, Jr. et al.

[ 51 July 18,1972

Inventors:

Assignee:

Filed:

Appl. No.:

Philip A. Dinenno, Jr., Glenriddle; Joseph S. Bonk, Philadelphia; Kenneth C. Conrad, Springfield; Rodney S. Moore, Broomall; Harry E. Lochman, Collingdale; Daniel D. Torello, Avondale, all of Pa.

Westinghouse Electric Corporation, Pittsburgh, Pa.

Dec. 8, 1970 .....415/l08, 415/151, 415/219 ..F0ld l/00, F04d 29/40 Field of Search ..415/105, 151, 199, 21 9 References Cited FOREIGN PATENTS OR APPLICATIONS 724,286 171935 France ..415/199 48,244 10/1937 France ..4 l 5/ l 99 95,102 6/1922 Switzerland .....4l5/199 197,873 5/1923 Great Britain... ..4l5/l99 Primary Examiner-Henry F. Raduazo Attorney--A. T. Stratton, F. P. Lyle and F. Cristiano, Jr.

[57] ABSTRACT In an elastic fluid turbine, an improved construction of the casing, the steam chest and the nozzle chamber which permits free expansion of parts subject to thermal transients at reduced cost and higher assurance of quality. This is accomplished by casting the nozzle chamber, the upper and lowe halves of the outer casing and at least a portion of the steam chest as separate pieces and then bolting them together. ln cases where a high pressure nozzle chamber is employed, this also is cast separate from the lower casing half and fitted into an opening in that part. Forming the assembly from a number of parts in this manner considerably reduces the problems encountered in casting complex shapes which are costly and difficult to fabricate.

6 Claims, 4 Drawing Figures Patented July 18, 1972 2 Sheets-Sheet 2 SPLIT CASTING STEAM CHEST, NOZZLE CHAMBER AND CASING ASSEMBLY FOR TURBINES BACKGROUND OF THE INVENTION While not limited thereto, the present invention is particularly adapted for use in steam turbines for boiler feed pump drives used in large central station power plants and the like. In such turbines, pressurized steam is supplied to a steam chest from where it passes through a valve assembly into passageways formed in a nozzle chamber and thence to noule groups, the latter being arranged in an annular array within the turbine casing and upstream of the first stage blading. The steam chest is provided with governor-controlled valves that are sequentially movable to open and close a plurality of flow paths between the steam chest and passageways formed in the nozzle chamber. During part-load operation, for example, some valves will be open; others will be closed; and steam will flow through only those passageways which are open to the nozzle chamber.

In steam turbines of this type for boiler feed pumps, the steam is usually taken from the main turbine-generator unit at the crossover pipe line of the low pressure turbine. The steam at this point varies in pressure downwardly from about 180 pounds per square inch, 650 F, and will support pumping power from 100 percent to about 40 percent main unit load. Below this, a secondary source of higher pressure steam must be available to the drive turbine or the system will collapse. This secondary source is usually from the cold reheat pipe line where the pressure varies downwardly from about 600 pounds per square inch, 750 F, or from the main boiler leads at a pressure in the range of about 2,400 to 3,500 pounds per square inch at 1,00? F.

Crossover steam is always admitted to the low pressure connection on the aforesaid steam chest. Cold reheat steam, pressure reduced and desuperheated if required, is either manifolded externally and connected to this same low pressure connection or to a separate high pressure inlet connection. When main boiler steam is selected as the secondary steam source, it is always connected to a separate high pressure inlet connection.

Due to the variety of steam sources, there are a multitude of temperature changes and differences that exist in the steam chest and nozzle areas. The low pressure nozzle chamber which is connected to the aforesaid valves through the steam chest is designed symmetrically about the turbine axis to assure even stress levels throughout. In some turbines, the low pressure nozzle chamber is inserted into a slot in the turbine casing such that its outside wall forms a wall of the turbine itself. In other designs, called double wall" designs,'the low pressure nozzle chamber connects to the turbine casing near the steam chest and is free to expand radially in the nozzle arch under rapidly varying temperatures within the individual nozzle chambers (from load changes) or with changing low pressure inlet temperatures (from steam source switching).

In most prior art turbines utilizing the double wall" construction, the steam chest, the low pressure nozzle chamber and the upper half of the casing are cast as an integral unit, the steam chest cover and the lower half of the casing being separate parts. A casting of this type (i.e., steam chest, low pressure nozzle chamber and upper casing half) is extremely complicated and difficult to cast. As a result, such castings are expensive and difficult to procure.

SUMMARY OF THE INVENTION In accordance with the present invention, a steam turbine inlet cylinder casing construction of the double-wall type is provided wherein the steam chest, nozzle chambers and casing cover are cast in separate pieces and then bolted together. Specifically, the assembly consists of a casing formed from upper and lower generally semicylindrical parts secured together by means of bolts or other suitable fastening means. An opening is provided in the upper wall of the upper casing part; and this opening receives a self-contained nozzle chamber including an annular array of nozzle groups and a cavernous body extending through the opening for conducting elastic fluid from the exterior to the interior of the casing. The cavernous body is spaced from the wall of the casing parts to permit relative thermal expansion and construction between the two; while means, preferably bolts, secure the top of the nozzle chamber to the periphery of the opening in the upper part.

In one embodiment of the invention shown herein, the steam chest is cast as a separate part and bolted to the upper end of the upper casing half; while in another embodiment the steam chest side walls are formed integrally with the nozzle chamber. In this latter case, the cover is bolted onto the open top of the steam chest.

In cases where a high pressure nozzle chamber is to be employed, such chamber is also cast as a separate part and inserted through an opening in the lower, outer casing part. Thus, instead of forming the turbine inlet casing assembly from essentially two extremely complicated castings as was the case in prior art constructions, the present invention facilitates the assembly of the inlet casing from four or five much simpler castings.

DESCRIPTION OF THE DRAWINGS The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIG. 1 is a transverse cross-sectional view of a steam turbine having an inlet casing and associated nozzle assembly constructed in accordance with the teachings of the invention;

FIG. 2 is a cross-sectional view taken substantially along line II-Il of FIG. 1;

FIG. 3 is a cross-sectional view of another embodiment of the invention; and

FIG. 4 is a cross-sectional view taken substantially along line IV-IV ofFIG. 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS With reference now to the drawings, and particularly to FIGS. 1 and 2, there is shown an axial flow steam turbine having a cylinder or casing 10, which casing is formed about a horizontal axis and includes an upper half 12 and a lower half 14 bolted together by means of bolts 15 passing through flanges l6.

Extending through an opening 18 (FIG. 2) in the upper casing part 12 is a low pressure nozzle chamber 20. The low pressure nozzle chamber 20 is provided with an upper peripheral flange 22 which is bolted by means of bolts 24 to a cooperating peripheral flange around the opening 18 on upper casing part 12. Also bolted to a flange 26 projecting outwardly from around the opening 18 is a separately cast steam chest 28 pro vided with openings 30 and 32 for the admission of steam from a suitable source, not shown.

In the upper wall of the low pressure nozzle chamber 20 is a plurality of openings 34 which receive valve seats 36. Each valve seat 36 is provided with a valve member 38 carried by a vertically movable, horizontal lift bar 40, only the valves on the left side of the assembly, the valve seats 36 and the lift bar 40 being shown in full lines in FIG. 1. The valve members 38 can slide within openings within the lift bar 40 and are provided with stop nuts 42 which, when engaged by the lift bar 40, will cause their associated valves to be unseated from their valve seats 36. Note that the valve member 38 closest to the center of the assembly will become unseated first, followed by successive unseating or opening of the remaining valve members until the outermost valve member is unseated. The arrangement of the right of center of FIG. 1 is identical to that to the left shown in full lines.

The steam in steam chest 28, after passing through one of the openings in a valve seat 36, passes into one of a plurality of passageways 44 cast into the low pressure nozzle chamber 20.

As shown in FIG. 2, each of the passageways 44 terminates at a nozzle vane assembly 46 which directs steam through rotatable blades 48 and stationary blades 50 carried on the turbine rotor 52 and the casing 26, respectively. The passageways 44, as best shown in FIG. 1, are formed between radially spaced walls 54 extending between the front and back walls of the low pressure nozzle chamber 20. As will be understood, under certain operating conditions, steam will be introduced into some of the passageways 44 and not others, giving rise to uneven thermal expansion forces. The arrangement shown permits portions of the walls 54 to elongate, due to thermal expansion, in a direction transverse to the rotor axis without imposing forces on other parts of the assembly. The outer wall of the nozzle chamber 20 is spaced from the casing 10, giving rise to a double wall construction. This permits relatively free expansion and contraction of the walls 54 of the nozzle chamber 20 without undue thermal stresses occasioned by the fact that the outer surface of the casing is exposed to ambient temperatures.

The lower casing part 14 is provided with an opening 56. Bolted to the periphery of this opening is a plate 58 having a central opening within which is welded or cast the neck portion of a high pressure nozzle chamber 60. The high pressure nozzle chamber 60, in turn, will be connected to the main boiler or to cold reheat steam as a secondary source through an intervening control and stop valve (not shown). In certain cases, it may not be necessary to employ the high pressure nozzle chamber 60, in which case the opening 56 will simply be closed by a plate, similar to plate 58 but without the high pressure nozzle chamber. The use of the high pressure nozzle chamber 60, however, provides the necessary flexibility required with high temperature steam admission and uses the same first row blading 48 used by the low pressure nozzle chamber 20. The low pressure nozzle chamber covers approximately 270 of the periphery of the rotor structure; while the high pressure nozzle assembly 60 covers the remaining 90, thus providing for maximum flow capacity from the design.

In prior art construction, this high pressure nozzle chamber 60 without plate 58 was welded directly to the periphery of a much smaller opening in base casing 14; however, this requires expensive X-ray quality chromium-molybdenum base castings. The bolted-on design permits the use of carbon steel material for the base casting without X-ray inspection. The nozzle chamber 60 is formed from a chromium-molybdenum steel.

It can thus be seen that a double wall inlet nozzle assembly is provided formed from four separate castings. The low pressure nozzle chamber 20 is a relatively small casting that can be poured in a horizontal position, improving metal feed at changes in section and minimizing cracks at these points. All external surfaces are accessible to facilitate inspection and repair. By isolating the complex nozzle chamber, the remaining parts become quite simple castings, lowering the cost per pound on the greater portion of the complete assembly. The use of a separately cast steam chest requires no boring or turning operations and need only be assembled at the final assembly stage. Boring operations involve the upper casing part 12, the lower casing part 14 and the nozzle chambers 20 and 60 only.

Another embodiment of the invention is shown in FIGS. 3 and 4. This embodiment is similar to that of FIGS. 1 and 2, and, accordingly, elements in FIGS. 3 and 4 which correspond to those of FIGS. 1 and 2 are identified by like reference numerals. In this case, however, and as best shown in FIG. 4, the side walls 28A and 28B of the steam chest 28 are cast integrally with the low pressure nozzle chamber 20. The upper ends of the walls 28A and 28B are provided with flanges 62 to which is bolted a covering plate 64. The chief advantage of the embodiment of FIGS. 3 and 4 over that of FIGS. 1 and 2 is that internal nozzle chamber bolting is not required. However, larger boring mills must be used to machine the castings shown in FIGS. 3 and 4.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

We claim as our invention:

1. An elastic fluid turbine comprising a casing formed from upper and lower generally semicylindrical parts secured together, an opening in the top wall of said upper part, a selfcontained nozzle chamber including an annular array of nozzle groups and a cavernous body extending through said opening for conducting elastic fluid from the exterior to the interior of the casing, said cavernous body being spaced from the walls of said casing parts to permit relative thermal expansion and contraction between the two, means securing the top of said body to the periphery of the opening in said upper part, a steam chest covering said top of the body and housing valve means for admitting steam under pressure to said nozzle chamber, means defining an opening in the bottom of said lower casing part, and a separately cast high pressure nozzle chamber inserted into and sealed within said opening.

2. The turbine recited in claim 1 wherein said steam chest comprises a separate casting which is bolted to the top of said upper part of said casing.

3. The turbine recited in claim I wherein the walls of said steam chest are cast integrally with said nozzle chamber, and further including a removable cover plate secured to the tops of the walls of said steam chest.

4. The turbine recited in claim 1 wherein said cavernous body defines passageways leading to nozzles, openings in the ends of said passageways opposite said nozzles, and valve means carried within said steam chest for controlling the admission of steam into said passageways through said openings.

5. The turbine recited in claim I and further including a flange extending around said opening in the top wall of said upper part, a flange around the upper edge of said nozzle chamber, and means securing said flanges together.

6. The turbine recited in claim 1 and further including a cover plate having an opening, said high pressure nozzle chamber being welded to said cover plate opening, and said cover plate fits over and covers said opening in the bottom of said lower casing part.

II at r 

1. An elastic fluid turbine comprising a casing formed from upper and lower generally semicylindrical parts secured together, an opening in the top wall of said upper part, a self-contained nozzle chamber including an annular array of nozzle groups and a cavernous body extending through said opening for conducting elastic fluid from the exterior to the interior of the casing, said cavernous body being spaced from the walls of said casing parts to permit relative thermal expansion and contraction between the two, means securing the top of said body to the periphery of the opening in said upper part, a steam chest covering said top of the body and housing valve means for admitting steam under pressure to said nozzle chamber, means defining an opening in the bottom of said lower casing part, and a separately cast high pressure nozzle chamber inserted into and sealed within said opening.
 2. The turbine recited in claim 1 wherein said steam chest comprises a separate casting which is bolted to the top of said upper part of said casing.
 3. The turbine recited in claim 1 wherein the walls of said steam chest are cast integrally with said nozzle chamber, and further including a removable cover plate secured to the tops of the walls of said steam chest.
 4. The turbine recited in claim 1 wherein said cavernous body defines passageways leading to nozzles, openings in the ends of said passageways opposite said nozzles, and valve means carried within said steam chest for controlling the admission of steam into said passageways through said openings.
 5. The turbine recited in claim 1 and further including a flange extending around said opening in the top wall of said upper part, a flange around the upper edge of said nozzle chamber, and means securing said flanges together.
 6. The turbine recited in claim 1 and further including a cover plate having an opening, said high pressure nozzle chamber being welded to said cover plate opening, and said cover plate fits over and covers Said opening in the bottom of said lower casing part. 